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Cope Rearrangement Induced by Medium-Sized Ring Strain.

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Table I . Selected physical data for the compounds 4b, 7 , rac-8, and ( - ) - 9 .
4b: Colorless, decomposable oil: IR (film)- I;=1655 c m - ' (C=C, enol ether). ' H - N M R (CDCI,): S=O.l5, 0.92 (2s, K H , -SiMeztBu), 1.5-3.72 (m,
I I H ) , 2.44 (s, 3 H , NCH.,), 3 28, 3.81 (each s, 9 H , OCH,), 4.24, 4.65 (2m.
2H), 5.02 (s, 2 H . CHJPh), 6.59, 6.60 (each s, 2 H , 5-, 8-Hj, 7.2-7.5 (m, 5 H ,
Ph): MS (70 eV): m / i 567 (I'Yo. M a ) , 282 (lOOo/u)
7 . Dark yellow oil: IR (film): S=3025 (vinyl. H), 1655 c m - ' (C=C, enol
ether); ' H - N M R (CDCI,): 6=0.15, 0.96 (each s, 15H, SiMe2tBu), 2.2-2.45
(m, 4 H , CH?), 2.37 (m, 1 H, CH), 3.24 (m, 2 H , CH2Br), 3.35 (s, 6 H , OCH,),
4.72 (d, I H, vinyl. H); MS (70 ev): m / z 366 (0.5%. M + I), 75 (100%)
rac-8: Yellow, viscous oil; UV(n-hexane):,lm.,,(lg&)=247 (4.2) nm: IR(tilm):
I;=1665 (C=O), 1655 c m - ' (enol ether); 'H-NMR (CDCI,): 6=0.13, 0.92
(each s, 15H, SiMe,tBu), 1.4-3.4 (m, 13H), 2.42 (5, 3 H , NCH,), 3.43, 3.52
(each s, 6 H , OCHI), 5.73 (s, I H, 5-H), 6.24 (s, I H, 8-H): MS (70 eV): m / z
445 (68%, M @ j
( - ) - 9 : M.p.= 197°C (ether); U V (methanol): ,l,,,(lg&)=276 (3.76). 240
(4.24) nm; IR (film): G=3555 (OH), 1670, 1645, 1622 c m - ' (cyclohexadienone); 'H-NMR (CDCI,) selected: 6 = 2.44 (s, 3 H, NCH,), 3.75,3.87 (each s,
6 H , OCH,), 6.31 (s, I H, 8-H), 6.69 (d, 5 = 7 . 0 Hz, I H, 1-HI, 6.74 (d, J = 7 . 0
Hz, I H, 2-H), 7.54 ( s , 1 H, 5-H); MS (70 ev): m / z 327 (100%. M " ) ; [a]?
-98" (c=0.55 g/IOO mL CH,OH), lit. 1141: [a]&'- 115" (c=0.55 g/IOO mL
CH?OH) for optically pure (-)-9
Received: July 4, 1986;
revised: August 5 , 1986 [Z 1844 I€]
German version: Angew. Chem. 98 (1986) 1032
CAS Registry numbers:
3a, 81763-87-3; 3b, 104779-65-9: 3c, 104779-66-0; 4a, 104779-63-7: 4b,
104779-64-8; 5 , 120-47-8; 6, 104779-68-2; 7, 104779.67-1 : (+)-8, 104779-69-3:
(+)-9, 23979-21-7: (-)-9,4090-18-0.
[ I ] G. Ehrhardt, H. Ruschig: Arzneimittel. Yo/. 1. p. 316, Verlag Chemie,
Weinheim 1968.
[2] a ) R. Grewe, W. Friedrichsen, Chem. Ber. 100 (1967) 1550: b) T. S. Lie,
L. Maat, H. C. Beyerman, R e d Trav Chim. Pays-Bas 98 (1979) 419 and
earlier work; c) K. C. Rice, J. Org. Chem. 45 (1980) 3135.
[3] a) D. H. R. Barton, D. S. Bhakuni, R. James, G. W. Kirby, J. Chem. Soc.
C 1967. 128; b) M. A. Schwartz, I. S. Mami, J. Am. Chem. SOC.97(1975)
1239; M. A. Schwartz, M. F. Zoda, J. Org. Chem. 46 (1981) 4625; c) C.
Szantay, G . Blasko, M. Barczai-Beke, P. Pechy, G. Dornyei, Tetrahedron
Lett. 21 (1980) 3509.
[4] a) L. L. Miller, R. F. Stewart, J. P. Gillespie, V. Ramachandran, Y . H.
So, R. F. Stermitz, J. Org. Chem. 43 (1978) 1580 and earlier work: b) E.
Kotani, S. Tobinata, Tetrahedron Lett. 1973. 4759; c) H. Kliinenberg, C.
Schaffer, H. J. Schafer, ibid. 23 (1982) 4581.
[ 5 ] D. A. Evans, C. H. Mitch, R. C. Thomas, D. M. Zimmerman, R. L. Robey, J. Am. Chem. SOC.102 (1980) 5955: D. A. Evans, C . H. Mitch, Tetrahedron Lett. 23 (1982) 285.
[6] a) M. Chandler, P. J. Parsons, J . Chem. SOC.Chem. Commun. 1984, 322:
b) A. G. Schultz, R. D. Lucci, J. J. Napier, H. Kinoshita, R. Ravichandran, P. Shannon, Y . K. Yee, J. Org. Chem. 50 (1985) 217.
[7] H. Klunenberg, Dissertation. Universitat Munster 1981.
181 By suitable substitution of the I-benzyl moiety with alkoxy groups it was
possible to carry out the coupling to give morphine precursors. Thus,
2-hydroxy-3-deoxythebainewas obtained from 1-(3.5-dibenzyloxybenzyl)-6,7-dimethoxy-2-trifluoroacetyl-I,2,3,4-tetrahydroisoquinolineby
means of anodic coupling in the key step: C. Schlegel, Dissertation. Universitat Miinster 1984.
[9] D. A. Evans, D. J. Hart, P. M. Koelsch, P. A. Cain, Pure Appl. Chem. 51
(1979) 1285.
[lo] a ) D. M. S. Wheeler, T. H. Kinstle, K. L. Rinehart, Jr., J . Am. Chem. SOC.
89 (1967) 4494; b) D. H. R. Barton, G. W. Kirby, W. Steglich, G. M.
Thomas, A. R. Battersby, T. A. Dobson, H. Ramuz, J . Chem. SOC.1965,
2423.
[ I l l a) J. D. White, G. Caravatti, T. B. Kline, E. Edstrom, K. C. Rice, A.
Brossi, Tetrahedron 39. 2393 (1983): b) K. C. Rice, J Med. Chem. 20
(1977) 164.
1121 K. W. Bentley i n R. H . F. Manske (Ed.): The Alkaloids. Vol. 13. Academic Press, New York 1971, p. 126.
[I31 a) A. I . Meyers, M. Boes, D. A. Dickman, Angew. Chem. 96 (1984) 448;
Angew. Chem. Inr. Ed. Engl. 23 (1984) 458; b) A. 1. Meyers, L. M.
Fuentes, Y. Kubota, Tetrahedron 40 (1984) 1361.
1141 T. Kametani, M. Ihara, K. Fukumoto, H. Yagi, J. Chem. Soc. Cl969,
2030.
I026
0 VCH Verlagsgesellschafr mbH. 0-6940 Weinherm. 1986
Cope Rearrangement Induced by Medium-sized Ring
Strain**
By Norbert Eisen and Fritz Vogtle*
In the case of small-ring compounds, Cope rearrangements can be facilitated considerably by Baeyer ring
strain."] We recently reported on degenerated rearrangements of Cope systems which are bridged on both sides by
long chains.l" Attempts to achieve strained hydrocarbons
in this way met with difficulties. By bridging only one side
of the biallyl system we have now succeeded in carrying
out a shorter bracketing and thus, for the first time, also a
Cope rearrangement in which the educt I is completely
converted-with ring expansion-into the product II by
virtue of the ring strain of a medium sized ring (Scheme 1).
Scheme I. B=bridge
Starting from the simple chalcone 3, readily obtainable
from the ketone 1 and benzaldehyde 2, the open-chain,
substituted tetraphenyl Cope system 9 was obtained via
the intermediates 4-8['] (data for the substances, see Table
1). Tetraaryl-substituted biallyl compounds of this type
first start to rearrange sigmatropically at temperatures
higher than are necessary for the synthesis ( < 85°C),[41i.e.
it can be assumed that 9 and not the Cope rearrangement
Br
MeOH
-0,.
0
1
3
2
BT
lINaBHL,MeOH
2162% HBr
HOAc
80 %
Br
BGGz=-Br
OHC
0
88 010
BT
X
\
\
L , X=OH
6
5, X=Br
I
Et,O
a, X=OH
96 o/o
9 , X=Br
11
[*I Prof. Dr. F. Vogtle, DipLChem. N. Eisen
lnstitut fur Organische Chemie und Biochemie der Universitat
Gerhard-Domagk-Strasse I , D-5300 Bonn I (FRG)
[**I This work was supported by the Deutsche Forschungsgemeinschaft. We
thank Dr. G . Eckhardt and Mr. C . Schmidt for help with the spectroscopic studies.
0S70-0833/86/1111-1026 $ 02 50/0
Angew. Chem. Int. Ed. Engl. 25 (1986) No. I 1
Table 1. Analytical data for the new compounds, all of whlch gave correct
high-resolution mass spectra a n d C,H analyses.
product 14 is formed under the conditions chosen for the
preparation of 9. A comparison of the 'H-NMR spectra
(benzyl and vinyl protons) of 9 and otherwise substituted
compounds prepared earlier1*"]show that 9 is formed as a
mixture of the meso- and d,l-conformational isomers (ca.
1 : I ) (Table 1).
Cyclization of meso-/d,l-9 with sodium sulfide in presence of cesium (Cs2C03, in ethanol, benzene)['] led to formation of the eleven-membered monosulfide 10, which,
however, could not be isolated; it isornerizes during workup to give the 15-membered isomer 11. This can be explained in terms of a ring strain-induced Cope rearrangement under the cyclization conditions (ca. 80°C, 8 h).I6]
Desulfurization of 11 was achieved photochemically in
triethyl phosphite as solvent (and thiophile),[" albeit at
higher temperatures than usual (60-80°C). This afforded
the 14-membered cyclic hydrocarbon 12.
The constitution of 11 and 12 follow from the COSY' H - N M R spectra (Table 1). In the case of the sulfide 11
the H, hydrogen atoms are not shifted upfield, whereas in
the case of the [6.2]rnetacyclophane 12 they are found at
somewhat higher field strength (6= 5.7). Signals are expected to be found at even higher field strength (6=4.6)
for the H , atoms in the case of the constitutionally isomeric
[2.2]metacyclophane 13; in the case of the sulfide 10, the
signals for the H, atoms should appear at 6 = 5.3, as indicated by a comparison with other cyclophane sulfides including the sulfide 15.[*]These findings also suggest that a
Cope rearrangement already takes place below 100°C in
the case of the suIfide 10, and that 12 is formed by photochemical desulfurization of 11 .I9] Apparently, the comparatively low ring strain of an eleven-membered [3.2]metacyclophane already suffices in order to shift the equilibrium
of the Cope rearrangement in favor of the larger, less
strained 15-membered ring.
Cpd.
M.p.
I"C1
'H-NMR (90 MHz, CDCIJTMS) 16 values]
92
7.26-7.2 (m. 9 aryl-H and 2 =CH)
oil
5.28 (d, J = 6 Hz, I -CH), 6.3 (dd, J = 16 and 6 Hz, 1
=CH), 6.66 (d, J = 16 Hz, 1 =CH), 7.08-8.1 (m, 9 arylH)
71
5.81 (d, J = 8 Hz, I -CH), 6.66 (m, 2 =CH), 7.17-7.68
(m, 9 aryl-H)
oil
3.82 (m, 2 -CH),6.2, 6.41 (m, 4 =CH, meso/d.l-form),
6.93-7.53 (m, 18 aryl-H)
oil
3.95 (m. 2 -CH), 6.24, 6.5 (m, 4 =CH, me.w/d,/-form).
7.05-7.88 (m, I8 aryl-H), 9.93, 10.0 (2 s , 2 CHO)
40
3.85 (m. 2 -CH), 4.33 (m, 2 CHIOH, 4H), 6.24. 6.44
(m, 4 =CH, meso/d,l-form), 6.88-7.42 (m, I8 aryl-H)
oil
3.84 (m, 2 -CH),4.33 (m, 2 CHIBr, 4H), 6.22. 6.44 (m,
4 =CH, mesdd.1-form), 6.95-7.38 (m, 18 aryl-H)
48
3.55 (s,4H,CH2-S-CHZ),3.80 (m.2 -CH).6.44 (m.4
=CH), 7.05-7.55 (m, 18 aryl-H)
I70
2.33, 3.1 (AB, 4 H , CHI-CH?, J n s = 9 Hz). 3.55 (dd,
J = 9 and 3 Hz, 2H), 5.7 (s, 2 H,), 5.8 (m, 2 =CH), 6.05
(d, 2 =CH, J = 15 Hz), 6.84-7.26 (m, 18 aryl-H)
193
3.1 (m, 2 H , -CH), 3.48, 3.69 (AB, 4 H , J A " = 14 Hz),
3.52, 3.88 (AB, 4 H , J,,B= 14 Hz), 5.35 ( s , 2 H,), 6.46 (m,
4 =CH), 7.05-7.44 (m. 16 Aryl-H)
[a] 'H-NMR at 200 MHz. [b] 'H-NMR at 400 MHz.
Received: July 7, 1986;
revised: July 21, 1986 [Z 1847 IE]
German version: Angew. Chem. 98 ( 1986) 1029
CAS Registry numbers:
1, 2142-63-4; 2, 100-52-7; 3, 25023-37-4; 4, 105065-87-0; 5, 105065-88-1 ;
meso4, 105065-89-2: rac-6, 105066-00-0: me.w7, 105065-90-5; roc-7, 10506601-1; meso-8, 105065-91-6; rac-8, 105066-02-2; meso-9, 105065-92-7; rac-9.
105065-93-8; 10, 105065-95-0; 11, 105065-94.9: 12, 105065-96-1 ; 14, 10506599-4; 15, 105065-98-3: 1,3,4,6-tetrdkis(3-bromomethylphenyl)1.5-hexadiene.
105065-97-2.
hv , PIOEtl3
11
5
O/O
12
S
14
13
15
The configuration (meso, d,I) of the products of the
Cope rearrangement cannot be derived with certainty from
the 'H-NMR spectra, since comparisons with known
open-chain biallyl systems are difficult owing to the extremely different conformational possibilities. Molecular
model considerations suggest that both diastereomers
(meso and d . 0 are possible with the size of the ring in 11.
Thus, for the first time, it has been confirmed experimentally that a Cope rearrangement to the less strained
product can be effected under mild conditions, not only by
the ring strain of three- and four-membered rings ("small
ring strain"), but also of medium sized rings. It now remains to explore the synthetic potential of this ring-expansion reaction (by four ring members). The possibility of
'fixing' conformations in the ground and transition state
thus opens u p new mechanistic aspects for sigmatropic
reactions.
Angew Chem.
Int.
Ed. Engl. 25 11986) No. I 1
[I] Review: G. Maier: Vuienzisomerbierungen. Verlag Chemie. Weinheim
1972. Cf. also: W. R. Roth, F.-G. Klarner, W. Grimme, H. G. Koser, R.
Busch, B. Muskulus, R. Breuckmann, B. P. Scholz, H.-W Lennartz,
Chem. Ber. 116 (1983) 2717, and references cited therein.
[2] F. Vogtle, N. Eisen, P. Mayenfels, F. Knoch, Terrahedron Leu. 27 (1986)
695.
131 On the basis of earlier studies and the conditions used we can rule out
allylic rearrangements of these compounds: D. Brombach, Dl.ssertafion.
Universitat Wiirzburg 1977; cf. [4cI.
[4] a) F. Vdgtle, E. Goldschmidt, Chem. Ber. 109 (1976) 1 ; b) the activation
parameters of tetraarylbiallyl compounds are: E,, = 127 kJ/mol,
A G + = 1 2 7 kJ/mol, A H f = 1 2 4 kJ/mol, A S f = -8.5 J / K mol. See c) D.
Brombach, F. Vogtle, Synthesis 1977. 800.
[5] W. Kissener, F. Vogtle, Angew. Chem. 97 (1985) 782: Angew Chem. Inr.
Ed. Engl. 24 (1985) 794.
[6] These conditions hold for the overall dilution principle reaction (9- 11).
Solutions of the bis(bromomethy1) compound 9 (2.00 mot) in benzene
(250 mL) and N a S . 9 H 2 0 in ethanol (250 mL) were added dropwise concurrently from separate dropping funnels within 8 h into 1.2 L of boiling
benzene/ethanol (2.5 : 1) containing 1.00 mmol of Cs2C03. The educt 9
reacts, according to our previous experience with similar reactions,
within a few minutes to give the cyclic sulfide. Neither time nor temperature suffice for a Cope rearrangement of the open-chain educt 9 I4bj. The
[3.2]phane 10 formed initially, however, has adequate time to undergo
Cope rearrangement under the reaction conditions.
171 K.-H. Duchene, F. Vogtle, Angew. Chem. 97 (1985) 867; Angew. Chem.
Int. Ed. Engl. 24 (1985) 885, and references cited therein.
[8] The his-sulfide 15 was obtained by reaction of the corresponding tetrakis(bromomethy1) compound with Na2S.9 H20/CsC0., in benzene/ethano1 (2 :1) in a dilution principle reaction, cf [2]. Yield: 36%1,for data see
Table 1.
[91 In the meantime, 12 has been obtained in 5% yield by direct phenyllithium cyclization from the bis(bromomethy1) compound 9 at 80°C. This
structural change 13- 12 is explained by a n intermediate Cope rearrangement.
0 VCH Verlagsgesellschaji mbH. 0-6940 Weinheim. 1986
0570-0833/86/111I-1027 $ 02.50/0
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